An optically semitransmissive film in a halftone phase-shift mask is an example of an optically semitransmissive film that partially transmits exposure light and in which the amount of phase shift is controlled.
A phase-shift mask is a photomask used in one type of super-resolution lithography in which photomasks are used in the lithographic step, which is one step in LSI manufacturing. Pattern contrast is improved by an interference effect (hereinafter referred to as the “phase-shift effect”) that is brought about by changing by 180° the phase of a portion of the light transmitted through the photomask. A halftone phase-shift mask is one type of phase-shift mask, and exposure light that passes through apertures with a prescribed dimension has an intensity distribution whose spread is greater than the dimensions of the apertures due to diffraction. The optical intensity of light *1 in the spread-out portion is cancelled out by the interference effect in which the light passes through the adjacent optically semitransmissive areas and interferes with light (interference light) whose phase is shifted by 180°, and the contrast of the boundary area of the two is increased.
Such halftone phase-shift masks are relatively easy to use in the manufacturing process, and are therefore the mainstream phase-shift masks currently used in KrF and ArF lithography. A single-layer thin film composed of Mo—Si—N is generally used as the material of the phase-shift film in a halftone phase-shift mask, the transmissivity is 5 to 15%, and the film thickness is about 60 nm to 100 nm.
A novel phase-shift mask is proposed in Patent Document 1. The mask is used to transfer a pattern that is compatible with a smaller LSI. This phase-shift mask transmits 15% or less of the exposure light and has a light-blocking film (optically semitransmissive film) that has a phase shift of (−30+360×m) degrees or more and (30+360×m) degrees or less (wherein m is an integer) between the light transmission areas. Also disclosed is a phase-shift mask provided with a phase shifter for generating a phase difference of (150+360×m) degrees or more and (210+360×m) or less (wherein m is an integer) in the apertures disposed in the light-blocking film.    Patent Document 1: Japanese Laid-open Patent Application No. 2003-21891